astrophysicist and science communicator

kepler

Since the first discoveries of planets outside of our own Solar System in the early 1990s, the quest has been on to find a “second Earth”. The number of candidate extrasolar planets detected has rocketed in recent years, thanks to dedicated missions and telescopes, such as WASP on the ground and Kepler in space. Today the number of exoplanet candidate detections stands at over 700, all found within my (25 year) lifetime.

This is obviously an exciting field in astronomy, both for the scientists actively working to discover and understand these exoplanets and for the public who, in a way, are seeing science fiction become reality (for some reason the quest for Earth in new Battlestar Galactica always comes to mind!). However, I do feel that some of the press releases (and subsequent news stories) that accompany these discoveries are clutching at straws slightly.

There seem to be two categories of extrasolar planets that the media love. One is the “Earth-like” planets. These are planets that astronomers believe to some characteristic that is similar to the Earth. It usually means that they are similar in size (i.e. radius) or mass. However, this can be deceiving. For example, the planet could be orbiting a pulsar or it could have a surface temperature of -200 degrees celsius! Earth-like doesn’t necessarily mean that we could live there. The second category of planets that get the media excited is the habitable, or Goldilocks, zone planets. A planet in the habitable zone is basically orbiting its star at the right distance for liquid water to exist on the surface. However, there’s nothing to say that these planets have to be rocky like the Earth, and gas planets have been found in habitable zones around stars. Of course, this is still interesting, especially if they have rocky moons (like Saturn’s moon Titan), but again, it’s something to bear in mind.

The first press release I could find claiming the discovery of an Earth-like planet was from ESO in April 2007. This press release announced the discovery of Gliese 581c and was titled “Astronomers Find First Earth-like Planet in Habitable Zone”.Gliese 581c is (unsurprisingly) orbiting around the star Gliese 581, a red dwarf star about 20 lightyears away from us. Because its host star doesn’t output as much energy as the Sun, Gliese 581c is much closer to its star than Earth is to the Sun and only takes about 13 days to complete an orbit. In case you were confused how this might affect the view on Gliese 581c, the Daily Mail helpfully included a cartoon in their report!

There have been so many “Earth-like” and habitable zone planets claimed recently that, as my officemate put it this morning, some of us are getting Earth-fatigue. I’m not sure who to blame for this. I would imagine that it’s the respective press offices of the universities or organisations trying to put a spin on the discoveries, and not the astronomers themselves. I guess it is important for us as scientists to let the public know what we are doing, after all they do fund (a lot of) us. Unfortunately this often requires a hook so you’d better hope that what you’ve found/are studying looks like food or is a giant gemstone in space. I just hope that when we do find a planet that is similar to Earth in size, mass, composition, atmosphere and is in the habitable zone, i.e. a true Earth 2.0 that we could live on (provided we could get there!), the public isn’t so sick of us crying wolf that they just don’t care.